How deep should the control joint be in a concrete slab?

The depth of the control joint in a concrete slab is ideally about one-quarter of the slab’s overall thickness. This depth strikes a balance, allowing the joint to effectively alleviate stresses that can lead to cracking while maintaining adequate structural integrity in the slab.

When you create control joints, they are meant to guide the natural cracking that occurs as concrete cures and dries. By cutting them to a depth of one-quarter of the slab thickness, you ensure that the joint is deep enough to allow for movement and cracking along the joint but not so deep that it compromises the structural performance of the slab as a whole.

Using a depth that is too shallow would not provide sufficient control over where the slab may crack. On the other hand, making the joint too deep could potentially weaken the structure, leading to other issues. Thus, one-quarter of the thickness is recognized as the most effective and sensible depth for control joints in concrete slabs.